Procedure for reinforcing a rock formation



June 20, 1967 c, w 1 Ms 3,326,004

E FOR REI Original Filed July 5, 1962 2 Sheets-Sheet 1 CHESTER I. WILLIAMS nnnnnn or June 20, 1967 c. WILLIAMS 3,326,004

PROCEDURE FOR REINFORCING A ROCK FORMATION Original Filed July 5 1962 2 Sheecs$heet 2 CHESTER I. WILLIAMS Inventor Arty.

United States Patent 3,326,004 PROCEDURE FOR REINFORCING A ROCK FORMATION Chester 1. Williams, 347 Greenbriar SE., Grand Rapids, Mich. 49506 Original application July 5, 1962, Ser. No. 207,488, now Patent No. 3,234,742, dated Feb. 15, 1966. Divided and this application Dec. 2, 1965, Ser. No. 511,146

3 Claims. (Cl. 61-35) This invention relates to the reinforcement of porous or fractured rock formations by filling the resulting spaces with grout injected under pressure. This application is a division of my application Ser. No. 207,488, filed July 5, 1962. The preferred form of this invention utilizes a hollow rock bolt as a conduit for the injected grout, with the obvious advantage of holding the formation in place against the hydraulic grout pressure. This feature is thus provided without requiring separate holes in the rock formation for both the bolt and the injection conduit. The procedure provides for sealing off the conduit hole with a preliminary injection so that full pressure can be delivered to the ultimate reinforcing charge.

The several features of the invention will be discussed in detail with reference to the accompanying drawing, in which:

FIGURE 1 is a sectional elevation showing the installation of a rock bolt in a bore in a rock formation, ready for grouting.

FIGURE 2 is a plan view of a bearing plate.

FIGURE 3 is -a plan view of a spacing ring.

FIGURE 4 presents a side elevation of a spacing ring.

FIGURE 5 presents an end view of a clip retaining the vent tube.

FIGURE 6 illustrates a portion of the assembly shown in FIGURE 1 after the completion of a grouting operation.

FIGURE 7 is a section on the plane 7-7 of FIG- URE 6.

Referring to the drawings, a rock formation is indicated generally at 10, and a bore 11 has been drilled into it with standard techniques that form no part of the present invention. A preferred form of rock bolt assembly is generally indicated at 12 and is positioned in the bore 11. The anchor device 13 has been se by rotation of the rod 14 so that it is in solid engagement with the walls of the bore 11. The anchor device 13 may be one of several types. The anchor 13 includes a hollow cored cone expander 13a in threaded engagement with the rod 14, and also includes a C-shaped expansion shell 13b, a thrust member 130 normally fixed with respect to the rod 14, and one or more lubricated slip rings 13d axially interposed between the thrust member and the expansion shell. The rod 14 is of conventional hollow construction so that it forms a conduit leading into the inner extremity of the bore 11. The rod also has a threaded end 15 engaged by a nut 16, and a spacing ring 17 establishes a spaced relationship between the nut 16 and a bearing plate 18. A plastic composition indicated at 19 is preferably inserted around the rod 14 after the anchor device 13 has been set, and after the surface tube 20 has been secured to the rod 14 with the clip 21. The clip is illustrated in FIGURE 5, and has the opposite resilient arms 22 and 23 embracing the rod 14, with the bight 24 engaging the tube 20. The clip may be moved axially into position along the rod 14, and thus installed after the rotation of the rod 14 has been completed. It is quite likely that there may not be sufficient lateral space at the entrance of the bore 11 to accommodate the engagement of the clip -21 from a lateral direction.

The opening 25 in the bearing plate 18 receives the rod 14 in the major portion 26 of the opening, and re- "ice ceives the tube 20 in the minor portion 27. This keyholeshaped opening establishes a position for the emergence of the tube 20 so that it will not be interfered with by the spacer ring 17 or the nut 16. The ring 17 may be beveled as shown in FIGURE 4 to accommodate an angular relationship between the axis of the bore 11 and the surface 27 of the rock formation. When the assembly has been arranged as shown in FIGURE 1, the grout may be pumped in at the end 28 of the tubular rod 14, and permitted to fill the bore 11 in the rock formation around the rod 14. Air will emerge through the tube 20, and a point will eventually be reached in which the grout 29 will itself emerge from the tube 20. The tube 20 and the rod 14 may be closed off so that the pressure of the grout within the bore may be maintained. Applicant has found that a very convenient method of accomplishing this closure is the application of pegs in the form of conventional golf tees at 30 and 31. These are left in place after the final injection of grout described below, at least until the grout has had a chance to set. On the hardening of the grout, a very secure bond will have been created between the roughened periphery of the conventional rod 14 and the surfaces of the bore 11. The tensile strength of the rod will be applied to hold the rock formation in place so that portions of it do not break away near the surface 27 The seams, exemplified in FIGURE 1 at 32, communicating with the bore 11 may be filled by using the rod 14 as a conduit. The preferred procedure for accomplishing this utilizes the surface tube 20 as the grout inlet. Grout is pumped in until the bore 11 is at least partially full, as determined either by control of the quantity of grout, or by the emergence of grout from the hollow rod 14. In the latter case, the tube should be plunged out by running a small rod through the hollow interior of the rod 14, or by blowing it out with compressed air, before the grout sets so that it may function as a conduit to the inner extremity of the bore 11. The grout surrounding the rod 14 is then permitted to set. The rod 14 is now prepared to function as a conduit, and grout may be pumped in through it to fill the interstices and seams in the formation. A grout pressure of 30 to pounds per square inch is commonly used, and the presence of the rock bolt will tend to hold the rock formation in place against the tremendous forces generated by the application of such pressures over large areas. The seal provided by the initial grout injection will also help to prevent local migration of grout to the surface during the later injection.

It is common to use rods 14 in lengths of five to fifteen feet in grouted installations; and where the secondary injection procedure described above is used, the inside diameter of the rod 14 should be approximately inch for a 1% inch rod, and inch for a 1% inch rod. Hightensile steel is recommended, as the required strength may be developed with less weight of material.

The particular embodiments of the present invention which have been illustrated and discussed herein are for illustrative purposes only and are not to be considered as a limitation upon the scope of the appended claims. In these claims, it is my intent to claim the entire invention disclosed herein, except as I am limited by the prior art.

I claim:

1. A procedure for reinforcing a rock formation, comprising:

drilling a hole in the said rock formation,

securing a hollow rock bolt in said hole;

injecting grout in said hole from a point adjacent the surface of said formation to partially fill the said hole including the portion of said hole adjacent said surface; and

injecting grout through said hollow rock bolt, after at least partial setting of the initial injection of grout, to fill the seams and interstices in the said formation communicating with said hole.

2. A procedure for reinforcing a rock formation, com

prising:

drilling a hole in the said rock formation;

securing a hollow rock bolt in said hole;

injecting grout in said hole from a point adjacent the surface of said formation to at least partially fill the said hole including the portion of said hole adjacent said surface; and

injecting grout through said hollow rock bolt, after setting of the initial injection of grout, to fill the seams and interstices in the said formation communicating with said hole.

3. A procedure for reinforcing a rock formation, comprising:

drilling a hole in the said rock formation; securing a rock bolt in said hole;

References Cited UNITED STATES PATENTS 2,667,037 1/1954 Thomas et a1. 61-45 2,682,152 6/1954 Bierer 61-45 FOREIGN PATENTS 84,93 8 1955 Norway.

CHARLES E. OCONNELL, Primary Examiner.

JACOB L. NACKENOFF, Examiner.

20 JACOB SHAPIRO, Assistant Examiner. 

1. A PROCEDURE FOR REINFORCING A ROCK FORMATION, COMPRISING: DRILLING A HOLE IN THE SAID ROCK FORMATION, SECURING A HOLLOW ROCK BOLT IN SAID HOLE; INJECTING GROUT IN SAID HOLE FROM A POINT ADJACENT THE SURFACE OF SAID FORMATION TO PARTIALLY FILL THE SAID HOLE INCLUDING THE PORTION OF SAID HOLE ADJACENT SAID SURFACE; AND INJECTING GROUT THROUGH SAID HOLLOW ROCK BOLT, AFTER AT LEAST PARTIAL SETTING OF THE INITIAL INJECTION OF GROUT, TO FILL THE SEAMS AND INTERSTICES IN THE SAID FORMATION COMMUNICATING WITH SAID HOLE. 